Dynamic implant fixation plate

ABSTRACT

The dynamic implant fixation plate and implant configured to accept the disclosed fixation plate can, in some aspects, provide a means of fixing an implant relative one or more planes while allowing motion relative to one or more planes. The use of the disclosed fixation plate and corresponding implant can reduce the occurrence of stress shielding and permit enhanced loading of the implant site.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/703,562 filed Jul. 26, 2018, which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to medical implants, and in particular tomedical implants using a fixation plate.

BACKGROUND OF THE INVENTION

Medical implants can be implanted in a fixed position within a bodythrough a variety of means. For example, bone fusion implants may beanchored to a patient's bone through the use of a bone screw.

BRIEF SUMMARY OF THE INVENTION

Disclosed herein is a dynamic implant fixation plate (hereinafter“fixation plate”) that can, in some embodiments, allow motion relativeto an implant after implantation. In some embodiments, the fixationplate can rotate or move relative to an implant and/or relative to apatient's tissue after implantation. In some embodiments, the fixationplate can allow axial compression relative to an implant afterimplantation. As used herein, the term “tissue” refers to any type ofbiological, natural or synthetic, tissue, including but not limited tomuscle tissue, epithelial tissue, connective tissue, nervous tissue andbony structures.

In the embodiment of the fixation plate presented, the fixation platecan be attached to the implant so that the fixation plate has at leastone degree of freedom relative to the implant. As used herein, a “degreeof freedom” refers to a direction in which independent motion may occur,however small that motion may be. The fixation plate can also beattached to a first bone and/or a second bone, each attachment with atleast one degree of freedom. In some embodiments, the fixation plate canbe attached to an implant and/or tissue so that the fixation plate hasmore than one degree of freedom relative to its respective attachmentpoint. In some embodiments, the fixation plate can be attached to afirst bone and/or a second bone with a conical degree of freedom.

Some embodiments of the fixation plate have screw holes with a concaveprofile and are attached to a patient's bone using a bone screw with ascrew head having a convex profile, corresponding to the concave profileof the screw holes, when viewed from the side on the end of the screwhead oriented towards the threaded portion. The use of a screw head witha convex profile and a screw hole with a concave profile can provide afixation with at least a conical degree of freedom. The bone screw headcan also be fixed relative to the fixation plate screw holes with aclearance fit of greater than zero that can provide, in some respects,an amount of translational motion and prevent binding between the bonescrew head and fixation plate screw holes.

The fixation plate can be attached to an implant using a fastening meanswith at least one degree of freedom. Some embodiments of the fixationplate use a fastening means with a clearance fit of greater than zerobetween the fixation plate and an implant that can provide, in somerespects, an amount of translational motion and prevent binding betweenthe fixation plate, the implant and/or the fastening means. Somefastening means that could be used include, but are not limited to,quarter turn fasteners, screws, etc.

The fixation plate can be configured for use in bone fusion implantswhere an implant is fixed to one or more bony structures. Attached usinganchors that allow at least one degree of freedom, the fixation platedoes not significantly hinder axial compression relative to the implant,where axial relative to the implant is the direction between a firstbone and a second bone. Some embodiments use at least a conical degreeof freedom to allow loading beyond that purely in the axial direction.

The disclosed fixation plate can be used in situations where it isdesirable to avoid stress shielding an implant. The use of a rigidattachment between an implant and a patient's bone can shield the newbone growth and existing bone from stress, resulting in weaker new bonegrowth and possible bone loss. The disclosed fixation plates transferthe load to the implant, rather than carrying the load, ensuring thatthe implant's modulus of elasticity and footprint largely determines theamount of axial compression allowed at the implant site.

Despite allowing axial movement, the disclosed fixation plate canadequately prevent lateral or fore and aft movement. When used with animplant that provides sufficient axial stability for new bone growth,the disclosed fixation plate can provide adequate stability indirections other than the axial to permit new bone to grow.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is an isometric view of a single modified rhombic dodecahedronunit cell containing a full modified rhombic dodecahedron structurealong with radial struts that comprise portions of adjacent unit cells.

FIG. 1B is a side view of a single modified rhombic dodecahedron unitcell showing the configuration of interconnections when viewed from alateral direction.

FIG. 1C is a side view of a single modified rhombic dodecahedron unitcell where the central void is being measured using the longestdimension method.

FIG. 1D is a side view of a single modified rhombic dodecahedron unitcell where an interconnection is being measured using the longestdimension method.

FIG. 1E is a side view of the central void of a modified rhombicdodecahedron unit cell being measured with the largest sphere method.

FIG. 1F is a view from a direction normal to the planar direction of aninterconnection being measured with the largest sphere method.

FIG. 1G is an isometric view of a single radial dodeca-rhombus unitcell.

FIG. 1H is a side view of a single radial dodeca-rhombus unit cell.

FIG. 1I is an isometric view of an example of a single node and singlestrut combination that could be used in a radial dodeca-rhombus unitcell.

FIG. 1J is a side view of an example of a single node and single strutcombination that could be used in a radial dodeca-rhombus unit cell.

FIG. 1K is a side view of a single node and single strut combinationconfigured for use in a lattice with an elastic modulus of approximately3 GPa, viewed from the corner of the volume defining the bounds of thecombination.

FIG. 1L is a side view of a single node and single strut combinationconfigured for use in a lattice with an elastic modulus of approximately4 GPa, viewed from the corner of the volume defining the bounds of thecombination.

FIG. 1M is a side view of a single node and single strut combinationconfigured for use in a lattice with an elastic modulus of approximately10 GPa, viewed from the corner of the volume defining the bounds of thecombination.

FIG. 1N is a side view of a single node and two adjacent struts viewedfrom the corner of the volume defining the bounds of the combination andthe lateral separation angle.

FIG. 1O is an isometric view of a sub-unit cell comprised of a singlenode and four struts.

FIG. 1P is an isometric view of two sub-unit cells in a stackedformation where the upper sub-unit cell is inverted and fixed to the topof the lower sub-unit cell.

FIG. 1Q is an isometric view of eight sub-unit cells stacked together toform a single unit cell.

FIG. 1R is a side view of a bone fixation plate, a bone screw and animplant.

FIG. 2 is an isometric view of a bone fixation plate, a bone screw andan implant.

FIG. 3 is an isometric view of a bone fixation plate and an implant.

FIG. 4 is a side view of a bone fixation plate and an implant.

FIG. 4A is a side view of the bone fixation plate and two bone screwswith hidden features shown in broken lines.

FIG. 5 is a side sectioned view of a bone fixation plate and an implant.

FIG. 6 is a rear view of a bone fixation plate and an implant.

FIG. 7 is a rear view of an implant configured to receive the bonefixation plate.

FIG. 8 is a side sectioned view of a bone fixation plate and an implant.

FIG. 9 is an isometric sectioned view of an implant configured toreceive the bone fixation plate.

FIG. 10 is a top sectioned view of an implant configured to receive thebone fixation plate.

DETAILED DESCRIPTION OF THE INVENTION

In many situations, it is desirable to use an implant that is capable ofbone attachment or osteointegration over time. It is also desirable inmany situations to use an implant that is capable of attachment orintegration with living tissue. Examples of implants where attachment tobone or osteointegration is beneficial include, but are not limited to,cervical, lumbar, and thoracic interbody fusion implants, vertebral bodyreplacements, osteotomy wedges, dental implants, bone stems, acetabularcups, cranio-facial plating, bone replacement and fracture plating. Inmany applications, it is also desirable to stress new bone growth toincrease its strength. According to Wolff s law, bone will adapt tostresses placed on it so that bone under stress will grow stronger andbone that isn't stressed will become weaker.

In some aspects, the systems and methods described herein can bedirected toward implants that are configured for osteointegration andstimulating adequately stressed new bone growth. Many of the exemplaryimplants of the present invention are particularly useful for use insituations where it is desirable to have strong bone attachment and/orbone growth throughout the body of an implant. Whether bone growth isdesired only for attachment or throughout an implant, the presentinvention incorporates a unique lattice structure that can providemechanical spacing, a scaffold to support new bone growth and a modulusof elasticity that allows new bone growth to be loaded withphysiological forces. As a result, the present invention providesimplants that grow stronger and healthier bone for more secureattachment and/or for a stronger bone after the implant osteointegrates.

The exemplary embodiments of the invention presented can be comprised,in whole or in part, of a lattice. A lattice, as used herein, refers toa three-dimensional material with one or more interconnected openingsthat allow a fluid to communicate from one location to another locationthrough an opening. A three-dimensional material refers to a materialthat fills a three-dimensional space (i.e. has height, width andlength). Lattices can be constructed by many means, including repeatingvarious geometric shapes or repeating random shapes to accomplish amaterial with interconnected openings. An opening in a lattice is anyarea within the bounds of the three-dimensional material that is devoidof that material. Therefore, within the three-dimensional boundaries ofa lattice, there is a volume of material and a volume that is devoid ofthat material.

The material that provides the structure of the lattice is referred toas the primary material. The structure of a lattice does not need toprovide structural support for any purpose, but rather refers to theconfiguration of the openings and interconnections that comprise thelattice. An opening in a lattice may be empty, filled with a gaseousfluid, filled with a liquid fluid, filled with a solid or partiallyfilled with a fluid and/or solid. Interconnections, with respect toopenings, refer to areas devoid of the primary material and that link atleast two locations together. Interconnections may be configured toallow a fluid to pass from one location to another location.

A lattice can be defined by its volumetric density, meaning the ratiobetween the volume of the primary material and the volume of voidspresented as a percentage for a given three-dimensional material. Thevolume of voids is the difference between the volume of the bounds ofthe three-dimensional material and the volume of the primary material.The volume of voids can comprise of the volume of the openings, thevolume of the interconnections and/or the volume of another materialpresent. For example, a lattice with a 30% volumetric density would becomprised of 30% primary material by volume and 70% voids by volume overa certain volume. A lattice with a 90% volumetric density would becomprised of 90% primary material by volume and 10% voids by volume overa certain volume. In three-dimensional materials with a volumetricdensity of less than 50%, the volume of the primary material is lessthan the volume of voids. While the volumetric density refers to thevolume of voids, the voids do not need to remain void and can be filled,in whole or in part, with a fluid or solid prior to, during or afterimplantation.

Lattices comprised of repeating geometric patterns can be describedusing the characteristics of a repeating unit cell. A unit cell in arepeating geometric lattice is a three-dimensional shape capable ofbeing repeated to form a lattice. A repeating unit cell can refer tomultiple identical unit cells that are repeated over a lattice structureor a pattern through all or a portion of a lattice structure. Each unitcell is comprised of a certain volume of primary material and a certainvoid volume, or in other words, a spot volumetric density. The spotvolumetric density may cover as few as a partial unit cell or aplurality of unit cells. In many situations, the spot volumetric densitywill be consistent with the material's volumetric density, but there aresituations where it could be desirable to locally increase or decreasethe spot volumetric density.

Unit cells can be constructed in numerous volumetric shapes containingvarious types of structures. Unit cells can be bound by a defined volumeof space to constrict the size of the lattice structure or other type ofstructure within the unit cell. In some embodiments, unit cells can bebound by volumetric shapes, including but not limited to, a cubicvolume, a cuboid volume, a hexahedron volume or an amorphous volume. Theunit cell volume of space can be defined based on a number of faces thatmeet at corners. In examples where the unit cell volume is a cubic,cuboid or hexahedron volume, the unit cell volume can have six faces andeight corners, where the corners are defined by the location where threefaces meet. Unit cells may be interconnected in some or all areas, notinterconnected in some or all areas, of a uniform size in some or allareas or of a nonuniform size in some or all areas. In some embodimentsdisclosed herein that use a repeating geometric pattern, the unit cellscan be defined by a number of struts defining the edges of the unit celland joined at nodes about the unit cell. Unit cells so defined can sharecertain struts among more than one unit cell, so that two adjacent unitcells may share a common planar wall defined by struts common to bothcells. In some embodiments disclosed herein that use a repeatinggeometric pattern, the unit cells can be defined by a node and a numberof struts extending radially from that node.

While the present application uses volumetric density to describeexemplary embodiments, it is also possible to describe them using othermetrics, including but not limited to cell size, strut size orstiffness. Cell size may be defined using multiple methods, includingbut not limited to cell diameter, cell width, cell height and cellvolume. Strut size may be defined using multiple methods, including butnot limited to strut length and strut diameter.

Repeating geometric patterns are beneficial for use in latticestructures contained in implants because they can provide predictablecharacteristics. Many repeating geometric shapes may be used as the unitcell of a lattice, including but are not limited to, rhombicdodecahedron, diamond, dodecahedron, square, pentagonal, hexagonal,octagonal, sctet struts, trunic octa, diagonal struts, other knowngeometric structures, and rounded, reinforced, weakened, or simplifiedversions of each geometry.

Lattices may also be included in implants as a structural component or anonstructural component. Lattices used in structural applications may bereferred to herein as structural lattices, load-bearing lattices orstressed lattices. In some instances, structural lattices, load-bearinglattices or stressed lattices may be simply referred to as a lattice.Repeating geometric shaped unit cells, particularly the rhombicdodecahedron, are well suited, in theory, for use in structural latticesbecause of their strength to weight ratio. To increase the actualstrength and fatigue resistance of a rhombic dodecahedron lattice, thepresent invention, in some embodiments, includes a modified strutcomprised of triangular segments, rather than using a strut with arectangular or circular cross section. Some embodiments herein alsomodify the angles defining the rhombic faces of a rhombic dodecahedronto change the lattice's elastic modulus and fatigue resistance. The useof triangular segments provides a lattice with highly predictableprinted properties that approach the theoretical strength values for arhombic dodecahedron lattice.

In structural lattice applications, the strength and elastic modulus ofthe lattice can be approximated by the volumetric density. When thevolumetric density increases, the strength and the elastic modulusincreases. Compared to other porous structures, the lattice of thepresent invention has a higher strength and elastic modulus for a givenvolumetric density because of its ability to use the high strength toweight benefits of a rhombic dodecahedron, modified rhombic dodecahedronor radial dodeca-rhombus unit cell.

The term “elastic modulus,” as used herein, can refer to either theelastic modulus of a material or the effective elastic modulus of avolume of material. An elastic modulus quantifies a material or volumeof material's resistance to elastic deformation in response to a stress.A volume of material can have an elastic modulus of the material itselfand an effective elastic modulus of the entire volume of material. Aneffective elastic modulus can be determined by compressing the volume ofmaterial and treating it as a homogenous material for the purposes ofcalculating the effective elastic modulus. When the term “elasticmodulus” is used herein, it can refer to both or either of the elasticmodulus of a material or the effective elastic modulus of a volume ofmaterial.

When configured to provide support for bone or tissue growth, a latticemay be referred to as a scaffold. Lattices can be configured to supportbone or tissue growth by controlling the size of the openings andinterconnections disposed within the three-dimensional material. Ascaffold, if used on the surface of an implant, may provide anosteointegration surface that allows adjacent bone to attach to theimplant. A scaffold may also be configured to provide a path that allowsbone to grow further than a mere surface attachment. Scaffolds intendedfor surface attachment are referred to herein as surface scaffolds. Asurface scaffold may be one or more unit cells deep, but does not extendthroughout the volume of an implant. Scaffolds intended to supportin-growth beyond mere surface attachment are referred to herein as bulkscaffolds. Scaffolds may also be included in implants as a structuralcomponent or a nonstructural component. Scaffolds used in structuralapplications may be referred to herein as structural scaffolds,load-bearing scaffolds or stressed scaffolds. In some instances,structural scaffolds, load-bearing scaffolds or stressed scaffolds maybe simply referred to as a scaffold. In some instances, the use of theterm scaffold may refer to a material configured to provide support forbone or tissue growth, where the material is not a lattice.

The scaffolds described herein can be used to promote the attachment orin-growth of various types of tissue found in living beings. As notedearlier, some embodiments of the scaffold are configured to promote boneattachment and in-growth. The scaffolds can also be configured topromote attachment of in-growth of other areas of tissue, such asfibrous tissue. In some embodiments, the scaffold can be configured topromote the attachment or in-growth of multiple types of tissue. Someembodiments of the scaffolds are configured to be implanted near orabutting living tissue. Near living tissue includes situations whereother layers, materials or coatings are located between a scaffold andany living tissue.

In some embodiments, the present invention uses bulk scaffolds withopenings and interconnections that are larger than those known in theart. Osteons can range in diameter from about 100 μm and it is theorizedthat a bundle of osteons would provide the strongest form of new bonegrowth. Bone is considered fully solid when it has a diameter of greaterthan 3 mm so it is theorized that a bundle of osteons with a diameterequaling approximately half of that value would provide significantstrength when grown within a scaffold. It is also theorized that osteonsmay grow in irregular shapes so that the cross-sectional area of anosteon could predict its strength. A cylindrical osteon growth with a 3mm diameter has a cross-sectional area of approximately 7 square mm anda cylindrical osteon with a 1.5 mm diameter has a cross-sectional areaof 1.8 square mm. It is theorized that an osteon of an irregular shapewith a cross-sectional area of at least 1.8 square millimeters couldprovide a significant strength advantage when grown in a scaffold.

Most skilled in the art would indicate that pores or openings with adiameter or width between 300 μm to 900 μm, with a pore side of 600 μmbeing ideal, provide the best scaffold for bone growth. Instead, someembodiments of the present invention include openings andinterconnections with a diameter or width on the order of 1.0 to 15.0times the known range, with the known range being 300 μm to 900 μm,resulting in openings from 0.07 mm² up to 145 mm² cross sectional areafor bone growth. In some examples, pores or openings with a diameter orwidth between and including 100 μm to 300 μm could be beneficial. Someexamples include openings and interconnections with a diameter on theorder of 1.0 to 5.0 times the known range. It has been at leasttheorized that the use of much larger openings and interconnections thanthose known in the art will allow full osteons and solid bone tissue toform throughout the bulk scaffold, allowing the vascularization of new,loadable bone growth. In some examples, these pores may be 3 mm indiameter or approximately 7 mm² in cross sectional area. In otherexamples, the pores are approximately 1.5 mm in diameter orapproximately 1.75 mm² in cross sectional area. The use of only thesmaller diameter openings and interconnections known in the art aretheorized to limit the penetration of new bone growth into a bulkscaffold because the smaller diameter openings restrict the ability ofvascularization throughout the bulk scaffold.

A related structure to a lattice is a closed cell material. A closedcell material is similar to a lattice, in that it has openings containedwithin the bounds of a three-dimensional material, however, closed cellmaterials generally lack interconnections between locations throughopenings or other pores. A closed cell structure may be accomplishedusing multiple methods, including the filling of certain cells orthrough the use of solid walls between the struts of unit cells. Aclosed cell structure can also be referred to as a cellular structure.It is possible to have a material that is a lattice in one portion and aclosed cell material in another. It is also possible to have a closedcell material that is a lattice with respect to only certaininterconnections between openings or vice versa. While the focus of thepresent disclosure is on lattices, the structures and methods disclosedherein can be easily adapted for use on closed cell structures withinthe inventive concept.

The lattice used in the present invention can be produced from a rangeof materials and processes. When used as a scaffold for bone growth, itis desirable for the lattice to be made of a biocompatible material thatallows for bone attachment, either to the material directly or throughthe application of a bioactive surface treatment. In one example, thescaffold is comprised of an implantable metal. Implantable metalsinclude, but are not limited to, zirconium, stainless steel (316 &316L), tantalum, nitinol, cobalt chromium alloys, titanium and tungsten,and alloys thereof. Scaffolds comprised of an implantable metal may beproduced using an additive metal fabrication or 3D printing process.Appropriate production processes include, but are not limited to, directmetal laser sintering, selective laser sintering, selective lasermelting, electron beam melting, laminated object manufacturing anddirected energy deposition.

In another example, the lattice of the present invention is comprised ofan implantable metal with a bioactive coating. Bioactive coatingsinclude, but are not limited to, coatings to accelerate bone growth,anti-thrombogenic coatings, anti-microbial coatings, hydrophobic orhydrophilic coatings, and hemophobic, superhemophobic, or hemophiliccoatings. Coatings that accelerate bone growth include, but are notlimited to, calcium phosphate, hydroxyapatite (“HA”), silicate glass,stem cell derivatives, bone morphogenic proteins, titanium plasma spray,titanium beads and titanium mesh. Anti-thrombogenic coatings include,but are not limited to, low molecular weight fluoro-oligomers.Anti-microbial coatings include, but are not limited to, silver,organosilane compounds, iodine and silicon-nitride. Superhemophobiccoatings include fluorinated nanotubes.

In another example, the lattice is made from a titanium alloy with anoptional bioactive coating. In particular, Ti6Al4V ELI wrought (AmericanSociety for Testing and Materials (“ASTM”) F136) is a particularlywell-suited titanium alloy for scaffolds. While Ti6Al4V ELI wrought isthe industry standard titanium alloy used for medical purposes, othertitanium alloys, including but not limited to, unalloyed titanium (ASTMF67), Ti6Al4V standard grade (ASTM F1472), Ti6Al7Nb wrought (ASTM 1295),Ti5Al2.5Fe wrought (British Standards Association/International StandardOrganization Part 10), CP and Ti6Al4V standard grade powders (ASTMF1580), Ti13Nb13Zr wrought (ASTM F1713), the lower modulusTi-24Nb-4Zr-8Sn and Ti12Mo6Zr2Fe wrought (ASTM F1813) can be appropriatefor various embodiments of the present invention.

Titanium alloys are an appropriate material for scaffolds because theyare biocompatible and allow for bone attachment. Various surfacetreatments can be done to titanium alloys to increase or decrease thelevel of bone attachment. Bone will attach to even polished titanium,but titanium with a surface texture allows for greater bone attachment.Methods of increasing bone attachment to titanium may be producedthrough a forging or milling process, sandblasting, acid etching, andthe use of a bioactive coating. Titanium parts produced with an additivemetal fabrication or 3D printing process, such as direct metal lasersintering, can be treated with an acid bath to reduce surface stressrisers, normalize surface topography, and improve surface oxide layer,while maintaining surface roughness and porosity to promote boneattachment.

Additionally, Titanium or other alloys may be treated with heparin,heparin sulfate (HS), glycosaminoglycans (GAG), chondroitin-4-sulphate(C4S), chondroitin-6-sulphate (C6S), hyaluronan (HY), and otherproteoglycans with or without an aqueous calcium solution. Suchtreatment may occur while the material is in its pre-manufacturing form(often powder) or subsequent to manufacture of the structure.

While a range of structures, materials, surface treatments and coatingshave been described, it is believed that a lattice using a repeatingmodified rhombic dodecahedron (hereinafter “MRDD”) unit cell can presenta preferable combination of stiffness, strength, fatigue resistance, andconditions for bone ingrowth. In some embodiments, the repeating MRDDlattice is comprised of titanium or a titanium alloy. A generic rhombicdodecahedron (hereinafter “RDD”), by definition, has twelve sides in theshape of rhombuses. When repeated in a lattice, an RDD unit cell iscomprised of 24 struts that meet at 14 vertices. The 24 struts definethe 12 planar faces of the structure and disposed at the center of eachplanar face is an opening, or interconnection, allowing communicationfrom inside the unit cell to outside the unit cell.

An example of the MRDD unit cell B10 used in the present invention isshown in FIGS. 1A-1E. In FIG. 1A is an isometric view of a single MRDDunit cell B10 containing a full MRDD structure along with radial strutsthat comprise portions of adjacent unit cells. In FIG. 1B is a side viewof a single MRDD unit cell B10 showing the configuration ofinterconnections when viewed from a lateral direction. A top or bottomview of the MRDD unit cell B10 would be substantially the same as theside view depicted in FIG. 1B. The MRDD unit cell B10 differs in bothstructural characteristics and method of design from generic RDD shapes.A generic RDD is comprised of 12 faces where each face is an identicalrhombus with an acute angle of 70.5 degrees and an obtuse angle of 109.5degrees. The shape of the rhombus faces in a generic RDD do not changeif the size of the unit cell or the diameter of the struts are changedbecause the struts are indexed based on their axis and each pass throughthe center of the 14 nodes or vertices.

In some embodiments of the MRDD, each node is contained within a fixedvolume that defines its bounds and provides a fixed point in space forthe distal ends of the struts. The fixed volume containing the MRDD or asub-unit cell of the MRDD can be various shapes, including but notlimited to, a cubic, cuboid, hexahedron or amorphous volume. Someexamples use a fixed volume with six faces and eight corners defined bylocations where three faces meet. The orientation of the struts can bebased on the center of a node face at its proximate end and the nearestcorner of the volume to that node face on its distal end. Each node ispreferably an octahedron, more specifically a square bipyramid (i.e. apyramid and inverted pyramid joined on a horizontal plane). Each node,when centrally located in a cuboid volume, more preferably comprises asquare plane parallel to a face of the cuboid volume, six vertices andis oriented so that each of the six vertices are positioned at theirclosest possible location to each of the six faces of the cuboid volume.Centrally located, with regards to the node's location within a volumerefers to positioning the node at a location substantially equidistantfrom opposing walls of the volume. In some embodiments, the node canhave a volumetric density of 100 percent and in other embodiments, thenode can have a volumetric density of less than 100 percent. Each faceof the square bipyramid node can be triangular and each face can providea connection point for a strut.

The struts can also be octahedrons, comprising an elongate portion ofsix substantially similar elongate faces and two end faces. The elongatefaces can be isosceles triangles with a first internal angle, angle A,and a second internal angle, angle B, where angle B is greater thanangle A. The end faces can be substantially similar isosceles trianglesto one another with a first internal angle, angle C, and a secondinternal angle, angle D, where angle D is greater than angle C.Preferably, angle C is greater than angle A.

The strut direction of each strut is a line or vector defining theorientation of a strut and it can be orthogonal or non-orthogonalrelative to the planar surface of each node face. In the MRDD and radialdodeca-rhombus structures disclosed herein, the strut direction can bedetermined using a line extending between the center of the strut endfaces, the center of mass along the strut or an external edge or face ofthe elongate portion of the strut. When defining a strut direction usinga line extending between the center of the strut end faces, the line isgenerally parallel to the bottom face or edge of the strut. Whendefining a strut direction using a line extending along the center ofmass of the strut, the line can be nonparallel to the bottom face oredge of the strut. The octahedron nodes of the MRDD can be scaled toincrease or decrease volumetric density by changing the origin point andsize of the struts. The distal ends of the struts, however, are lockedat the fixed volume corners formed about each node so that their anglerelative to each node face changes as the volumetric density changes.Even as the volumetric density of an MRDD unit cell changes, thedimensions of the fixed volume formed about each node does not change.In FIG. A1, dashed lines are drawn between the corners of the MRDD unitcell B10 to show the cube B11 that defines its bounds. In the MRDD unitcell in FIG. A1, the height B12, width B13 and depth B14 of the unitcell are substantially the same, making the area defined by B11 a cube.

In some embodiments, the strut direction of a strut can intersect thecenter of the node and the corner of the cuboid volume nearest to thenode face where the strut is fixed. In some embodiments, the strutdirection of a strut can intersect just the corner of the cuboid volumenearest to the node face where the strut is fixed. In some embodiments,a reference plane defined by a cuboid or hexahedron face is used todescribe the strut direction of a strut. When the strut direction of astrut is defined based on a reference plane, it can be between 0 degreesand 90 degrees from the reference plane. When the strut direction of astrut is defined based on a reference plane, it is preferably eightdegrees to 30 degrees from the reference plane.

By indexing the strut orientation to a variable node face on one end anda fixed point on its distal end, the resulting MRDD unit cell can allowrhombus shaped faces with a smaller acute angle and larger obtuse anglethan a generic RDD. The rhombus shaped faces of the MRDD can have twosubstantially similar opposing acute angles and two substantiallysimilar opposing obtuse angles. In some embodiments, the acute anglesare less than 70.5 degrees and the obtuse angles are greater than 109.5degrees. In some embodiments, the acute angles are between 0 degrees and55 degrees and the obtuse angles are between 125 degrees and 180degrees. In some embodiments, the acute angles are between 8 degrees and60 degrees and the obtuse angles are between 120 degrees and 172degrees. The reduction in the acute angles increases fatigue resistancefor loads oriented across the obtuse angle corner to far obtuse anglecorner. The reduction in the acute angles and increase in obtuse anglesalso orients the struts to increase the MRDD's strength in shear andincreases the fatigue resistance. By changing the rhombus corner anglesfrom a generic RDD, shear loads pass substantially in the axialdirection of some struts, increasing the shear strength. Changing therhombus corner angles from a generic RDD also reduces overall deflectioncaused by compressive loads, increasing the fatigue strength byresisting deflection under load.

When placed towards the center of a lattice structure, the 12interconnections of a unit cell connect to 12 different adjacent unitcells, providing continuous paths through the lattice. The size of thecentral void and interconnections in the MRDD may be defined using thelongest dimension method as described herein. Using the longestdimension method, the central void can be defined by taking ameasurement of the longest dimension as demonstrated in FIG. 1C. In FIG.1C, the longest dimension is labeled as distance AA. The distance AA canbe taken in the vertical or horizontal directions (where the directionsreference the directions on the page) and would be substantially thesame in this example. The interconnections may be defined by theirlongest measurement when viewed from a side, top or bottom of a unitcell. In FIG. 1D, the longest dimension is labeled as distance AB. Thedistance AB can be taken in the vertical or horizontal directions (wherethe directions reference the directions on the page). The view in FIG.1D is a lateral view, however, in this example the unit cell will appearsubstantially the same when viewed from the top or bottom.

The size of the central void and interconnections can alternatively bedefined by the largest sphere method as described herein. Using thelargest sphere method, the central void can be defined by the diameterof the largest sphere that can fit within the central void withoutintersecting the struts. In FIG. 1E is an example of the largest spheremethod being used to define the size of a central void with a spherewith a diameter of BA. The interconnections are generally rhombus shapedand their size can alternatively be defined by the size of the lengthand width of three circles drawn within the opening. Drawn within theplane defining a side, a first circle BB1 is drawn at the center of theopening so that it is the largest diameter circle that can fit withoutintersecting the struts. A second circle BB2 and third circle BB3 isthem drawn so that they are tangential to the first circle BB1 and thelargest diameter circles that can fit without intersecting the struts.The diameter of the first circle BB1 is the width of the interconnectionand the sum of the diameters of all three circles BB1, BB2 & BB3represents the length of the interconnection. Using this method ofmeasurement removes the acute corners of the rhombus shaped opening fromthe size determination. In some instances, it is beneficial to removethe acute corners of the rhombus shaped opening from the calculated sizeof the interconnections because of the limitations of additivemanufacturing processes. For example, if an SLS machine has a resolutionof 12 μm where the accuracy is within 5 μm, it is possible that theacute corner could be rounded by the SLS machine, making it unavailablefor bone ingrowth. When designing lattices for manufacture on lessprecise additive process equipment, it can be helpful to use thismeasuring system to better approximate the size of the interconnections.

Using the alternative measuring method, in some examples, the width ofthe interconnections is approximately 600 μm and the length of theinterconnections is approximately 300 μm. The use of a 600 μm length and300 μm width provides an opening within the known pore sizes for bonegrowth and provides a surface area of roughly 1.8 square millimeters,allowing high strength bone growth to form. Alternative embodiments maycontain interconnections with a cross sectional area of 1.0 to 15.0times the cross-sectional area of a pore with a diameter of 300 μm.Other embodiments may contain interconnections with a cross sectionalarea of 1.0 to 15.0 times the cross-sectional area of a pore with adiameter of 900 μm.

The MRDD unit cell also has the advantage of providing at least two setsof substantially homogenous pore or opening sizes in a latticestructure. In some embodiments, a first set of pores have a width ofabout 200 μm to 900 μm and a second set of pores have a width of about 1to 15 times the width of the first set of pores. In some embodiments, afirst set of pores can be configured to promote the growth ofosteoblasts and a second set of pores can be configured to promote thegrowth of osteons. Pores sized to promote osteoblast growth can have awidth of between and including about 100 μm to 900 μm. In someembodiments, pores sized to promote osteoblast growth can have a widththat exceeds 900 μm. Pores sized to promote the growth of osteons canhave a width of between and including about 100 μm to 13.5 mm. In someembodiments, pores sized to promote osteon growth can have a width thatexceeds 13.5 mm.

In some embodiments, it is beneficial to include a number ofsubstantially homogenous larger pores and a number of substantiallyhomogenous smaller pores, where the number of larger pores is selectedbased on a ratio relative to the number of smaller pores. For example,some embodiments have one large pore for every one to 25 small pores inthe lattice structure. Some embodiments preferably have one large porefor every eight to 12 smaller pores. In some embodiments, the number oflarger and smaller pores can be selected based on a percentage of thetotal number of pores in a lattice structure. For example, someembodiments can include larger pores for four percent to 50 percent ofthe total number of pores and smaller pores for 50 percent to 96 percentof the total number of pores. More preferably, some embodiments caninclude larger pores for about eight percent to 13 percent of the totalnumber of pores and smaller pores for about 87 percent to 92 percent ofthe total number of pores. It is believed that a lattice constructedwith sets of substantially homogenous pores of the disclosed two sizesprovides a lattice structure that simultaneously promotes osteoblast andosteon growth.

The MRDD unit cell may also be defined by the size of theinterconnections when viewed from a side, top or bottom of a unit cell.The MRDD unit cell has the same appearance when viewed from a side, topor bottom, making the measurement in a side view representative of theothers. When viewed from the side, as in FIG. 1D, an MRDD unit celldisplays four distinct diamond shaped interconnections withsubstantially right angles. The area of each interconnection is smallerwhen viewed in the lateral direction than from a direction normal to theplanar direction of each interconnection, but the area when viewed inthe lateral direction can represent the area available for bone to growin that direction. In some embodiments, it may be desirable to index theproperties of the unit cell and lattice based on the area of theinterconnections when viewed from the top, bottom or lateral directions.

In some embodiments of the lattice structures disclosed herein, thecentral void is larger than the length or width of the interconnections.Because the size of each interconnection can be substantially the samein a repeating MRDD structure, the resulting lattice can be comprised ofopenings of at least two discrete sizes. In some embodiments, it ispreferable for the diameter of the central void to be approximately twotimes the length of the interconnections. In some embodiments, it ispreferable for the diameter of the central void to be approximately fourtimes the width of the interconnections.

In some embodiments, the ratio between the diameter of the central voidand the length or width of the interconnections can be changed to createa structural lattice of a particular strength. In these embodiments,there is a correlation where the ratio between the central void diameterand the length or width of the interconnections increases as thestrength of the structural lattice increases.

It is also believed that a lattice using a repeating radialdodeca-rhombus (hereinafter “RDDR”) unit cell can present a preferablecombination of stiffness, strength, fatigue resistance, and conditionsfor bone ingrowth. In some embodiments, the repeating RDDR lattice iscomprised of titanium or a titanium alloy. In FIG. 1G is an isometricview of a single RDDR unit cell B20 containing a full RDDR structure. InFIG. 1H is a side view of a single RDDR unit cell B20 showing theconfiguration of interconnections when viewed from a lateral direction.A top or bottom view of the RDDR unit cell B20 would be substantiallythe same as the side view depicted in FIG. 1H.

As used herein, an RDDR unit cell B20 is a three-dimensional shapecomprised of a central node with radial struts and mirrored strutsthereof forming twelve rhombus shaped structures. The node is preferablyan octahedron, more specifically a square bipyramid (i.e. a pyramid andinverted pyramid joined on a horizontal plane). Each face of the node ispreferably triangular and fixed to each face is a strut comprised of sixtriangular facets and two end faces. The central axis of each strut canbe orthogonal or non-orthogonal relative to the planar surface of eachnode face. The central axis may follow the centroid of the strut. TheRDDR is also characterized by a central node with one strut attached toeach face, resulting in a square bipyramid node with eight strutsattached.

Examples of node and strut combinations are shown in FIGS. 1I-1M. InFIG. 1I is an isometric view of a single node B30 with a single strutB31 attached. The node B30 is a square bipyramid oriented so that twopeaks face the top and bottom of a volume B32 defining the bounds of thenode B30 and any attached strut(s) B31. The node B30 is oriented so thatthe horizontal corners are positioned at their closest point to thelateral sides of the volume B32. The strut B31 extends from a node B30face to the corner of the volume B32 defining the bounds of the node andattached struts. In FIG. 1I, the central axis of the strut is 45 degreesabove the horizontal plane where the node's planar face is 45 degreesabove a horizontal plane.

FIG. 1I also details an octahedron strut B31, where dashed lines showhidden edges of the strut. The strut B31 is an octahedron with anelongate portion of six substantially similar elongate faces and two endfaces. The elongate faces B31 a, B31 b, B31 c, B31 d, B31 e & B31 f ofthe strut B31 define the outer surface of the strut's elongate andsomewhat cylindrical surface. Each of the elongate faces B31 a, B31 b,B31 c, B31 d, B31 e & B31 f are isosceles triangles with a firstinternal angle, angle A, and a second internal angle, angle B, whereangle B is greater than angle A. The strut B31 also has two end facesB31 f & B31 g that isosceles triangles that are substantially similar toone another, having a first internal angle, angle C, and a secondinternal angle, angle D, and where angle D is greater than angle C. Whencomparing the internal angles of the elongate faces B31 a, B31 b, B31 c,B31 d, B31 e & B31 f to the end faces B31 f & B31 g, angle C is greaterthan angle A.

In FIG. 1J is a side view of the node B30 and strut B31 combinationbounded by volume B32. In the side view, the height of the node B30compared to the height of the cube B32 can be compared easily. In FIGS.1K-1M are side views of node and strut combinations viewed from a cornerof the volume rather than a wall or face, and where the combinationshave been modified from FIGS. 1I-1J to change the volumetric density ofthe resulting unit cell. In FIG. 1K, the height of the node B130 hasincreased relative to the height of the volume B132. Since the distalend of the strut B131 is fixed by the location of a corner of the volumeB132, the strut B131 must change its angle relative to its attached nodeface so that it becomes nonorthogonal. The node B130 and strut B131combination, where the angle of the strut B131 from a horizontal planeis about 20.6 degrees, would be appropriate for a lattice structure withan elastic modulus of approximately 3 GPa.

In FIG. 1L, the height of the node B230 relative to the height of thecube B232 has been increased over the ratio of FIG. 1K to create a nodeB230 and strut B231 combination that would be appropriate for a latticestructure with an elastic modulus of approximately 4 GPa. As the heightof the node B230 increases, the angle between the strut B231 and ahorizontal plane decreases to about 18.8 degrees. As the height of thenode B230 increases, the size of the node faces also increase so thatthe size of the strut B231 increases. While the distal end of the strutB231 is fixed to the corner of the volume B232, the size of the distalend increases to match the increased size of the node face to maintain asubstantially even strut diameter along its length. As the node andstrut increase in size, the volumetric density increases, as does theelastic modulus. In FIG. 1M, the height of the node B330 relative to theheight of the volume B332 has been increased over the ratio of FIG. 1Mto create a node B330 and strut B331 combination that would beappropriate for a lattice structure with an elastic modulus ofapproximately 10 GPa. In this configuration, the angle B333 between thestrut B331 and a horizontal plane decreases to about 12.4 degrees andthe volumetric density increases over the previous examples. The singlenode and strut examples can be copied and/or mirrored to create unitcells of appropriate sizes and characteristics. For instance, the anglebetween the strut and a horizontal plane could be increased to 25.8degrees to render a lattice with a 12.3 percent volumetric density andan elastic modulus of about 300 MPa. While a single node and singlestrut were shown in the examples for clarity, multiple struts may beattached to each node to create an appropriate unit cell.

Adjacent struts extending from adjacent node faces on either the upperhalf or lower half of the node have an angle from the horizontal planeand a lateral separation angle defined by an angle between the strutdirections of adjacent struts. In the MRDD and RDDR structures, adjacentstruts have an external edge or face of the elongate portion extendingclosest to the relevant adjacent strut. The lateral separation angle, asused herein, generally refers to the angle between an external edge orface of the elongate portion of a strut extending closest to therelevant adjacent strut. In some embodiments, a lateral separation angledefined by a line extending between the center of the strut end faces ora line defined by the center of mass of the struts can be used inreference to a similar calculation for an adjacent strut.

The lateral separation angle is the angle between the nearest face oredge of a strut to an adjacent strut. The lateral separation angle canbe measured as the smallest angle between the nearest edge of a strut tothe nearest edge of an adjacent strut, in a plane containing both strutedges. The lateral separation angle can also be measured as the anglebetween the nearest face of a strut to the nearest face of an adjacentstrut in a plane normal to the two strut faces. In embodiments withoutdefined strut edges or strut faces, the lateral separation angle can bemeasured as an angle between the nearest portion of one strut to thenearest portion of an adjacent strut. For a unit cell in a cubic volume,as the strut angle from the horizontal plane decreases, the lateralseparation angle approaches 90 degrees. For a unit cell in a cubicvolume, as the strut angle from the horizontal plane increases, thelateral separation angle approaches 180 degrees. In some embodiments, itis preferable to have a lateral separation angle greater than 109.5degrees. In some embodiments, it is preferable to have a lateralseparation angle of less than 109.5 degrees. In some embodiments, it ispreferable to have a lateral separation angle of between and includingabout 108 degrees to about 156 degrees. In some embodiments, it is morepreferable to have a lateral separation angle of between and including111 degrees to 156 degrees. In some embodiments, it is more preferableto have a lateral separation angle of between and including 108 degreesto 120 degrees. In some embodiments, it is most preferable to have alateral separation angle of between and including about 111 degrees to120 degrees. In some embodiments, it is more preferable to have alateral separation angle of between and including 128 degrees to 156degrees. In FIG. 1N is a side view, viewed from a corner of the cubeB432, of a single node B430 with two adjacent struts B431 & B434attached and where the lateral separation angle B443 is identified. Whenmeasured from the nearest edge of a strut to the nearest edge of anadjacent strut, the lateral separation angle B443 is about 116 degrees.

In some embodiments, a unit cell is built up from multiple sub-unitcells fixed together. In FIG. 1O is an isometric view of an exemplarysub-unit cell comprising a single node and four struts. In FIG. A16 isan isometric view of two sub-unit cells in a stacked formation where theupper sub-unit cell is inverted and fixed to the top of the lowersub-unit cell. In FIG. 1Q is an isometric view of eight sub-unit cellsstacked together to form a single RDDR unit cell.

In FIG. 1O, the node B530 is a square bipyramid, oriented so that thetwo peaks face the top and bottom of a cubic volume B532. In someembodiments, the volume B532 can be a cuboid volume, a hexahedronvolume, an amorphous volume or of a volume with one or morenon-orthogonal sides. The peaks refer to the point where four upperfaces meet and the point where four lower faces meet. The node B530 isoriented so that the horizontal vertices face the lateral sides of thecubic volume B532. The strut B531 is fixed to a lower face of the nodeB530 face on its proximate end and extends to the nearest corner of thecubic volume B532 at its distal end. The distal end of the strut B531can remain fixed to the cubic volume B532 even if the node B530 changesin size to adjust the sub-unit cell properties.

On the lower face of the node B530 opposite the face which strut B531 isfixed, the proximate end of strut B534 is fixed to the node B530. Thestrut B534 extends to the nearest corner of cubic volume B532 at itsdistal end. The strut B535 is fixed on its proximate end to an uppernode B530 face directed about 90 degrees laterally from the node B530face fixed to strut B531. The strut B535 extends to the nearest cornerof the cubic volume B532 at its distal end. On the upper face of thenode B530 opposite the face which strut B535 is fixed, the proximate endof strut B536 is fixed to the node B530. The strut B536 extends to thenearest corner of the cubic volume B532 at its distal end.

In some embodiments, the struts B531 & B534-B536 are octahedrons withtriangular faces. The strut face fixed to a node B530 face can besubstantially the same size and orientation of the node B530 face. Thestrut face fixed to the nearest corner of the cube B532 can besubstantially the same size as the strut face fixed to the node B530 andoriented on a substantially parallel plane. The remaining six faces canbe six substantially similar isosceles triangles with a first internalangle and a second internal angle larger than said first internal angle.The six substantially similar isosceles triangles can be fixed alongtheir long edges to an adjacent and inverted substantially similarisosceles triangle to form a generally cylindrical shape with triangularends.

When forming a sub-unit cell B540, it can be beneficial to add an eighthnode B538 to each corner of the cube B532 fixed to a strut B531 &B534-B536. When replicating the sub-unit cell B540, the eighth node B538attached to each strut end is combined with eighth nodes from adjacentsub-unit cells to form nodes located between the struts of adjacentsub-unit cells.

In FIG. A16 is a first sub-unit cell B540 fixed to a second sub-unitcell B640 to form a quarter unit cell B560 used in some embodiments. Thesecond sub-unit cell B640 comprises a square bipyramid node B630 is asquare bipyramid, oriented so that the two peaks face the top and bottomof a cubic volume. The node B630 is oriented so that the horizontalvertices face the lateral sides of the cubic volume. The strut B635 isfixed to a lower face of the node B630 face on its proximate end andextends to the nearest corner of the cubic volume at its distal end. Onthe lower face of the node B630 opposite the face which strut B635 isfixed, the proximate end of strut B636 is fixed to the node B630. Thestrut B636 extends to the nearest corner of cubic volume at its distalend. The strut B634 is fixed on its proximate end to an upper node B630face directed about 90 degrees laterally from the node B630 face fixedto strut B635. The strut B634 extends to the nearest corner of the cubicvolume at its distal end. On the upper face of the node B630 oppositethe face which strut B634 is fixed, the proximate end of strut B631 isfixed to the node B630. The strut B631 extends to the nearest corner ofthe cubic volume at its distal end.

The first sub-unit B540 is used as the datum point in the embodiment ofFIG. A16, however, it is appreciated that the second sub-unit cell B640or another point could also be used as the datum point. Once the firstsub-unit cell B540 is fixed in position, it is replicated so that thesecond sub-unit cell B640 is substantially similar to the first. Thesecond sub-unit cell B640 is rotated about its central axis prior tobeing fixed on the top of the first unit-cell B540. In FIG. A16, thesecond sub-unit cell B640 is inverted to achieve the proper rotation,however, other rotations about the central axis can achieve the sameresult. The first sub-unit cell B540 fixed to the second sub-unit cellB640 forms a quarter unit cell B560 that can be replicated and attachedlaterally to other quarter unit cells to form a full unit cell.

Alternatively, a full unit cell can be built up by fixing a first groupof four substantially similar sub-unit cells together laterally to forma square, rectangle or quadrilateral when viewed from above. A secondgroup of four substantially similar sub-unit cells rotated about theircentral axis can be fixed together laterally to also form a square,rectangle or quadrilateral when viewed from above. The second group ofsub-unit cells can be rotated about their central axis prior to beingfixed together laterally or inverted after being fixed together toachieve the same result. The second group is then fixed to the top ofthe first group to form a full unit cell.

In FIG. 1Q is an example of a full unit cell B770 formed by replicatingthe sub-unit cell B540 of FIG. 1O. The cube B532 defining the bounds ofthe sub-unit cell B540 is identified as well as the node B530 and strutsB531 & B534-B536 for clarity. The full unit cell B770 of FIG. 1Q can beformed using the methods described above or using variations within theinventive concept.

Each strut extending from the node, for a given unit cell, can besubstantially the same length and angle from the horizontal plane,extending radially from the node. At the end of each strut, the strut ismirrored so that struts extending from adjacent node faces form arhombus shaped opening. Because the struts can be non-orthogonal to thenode faces, rhombuses of two shapes emerge. In this configuration, afirst group of four rhombuses extend radially from the node oriented invertical planes. The acute angles of the first group of rhombuses equaltwice the strut angle from the horizontal plane and the obtuse anglesequal 180 less the acute angles. Also in this configuration is a secondgroup of eight rhombuses extending radially so that a portion of thesecond group of eight rhombuses fall within the lateral separation anglebetween adjacent struts defining the first group of four rhombuses. Theacute angles of the second group of rhombuses can be about the same asthe lateral separation angle between adjacent struts that define thefirst group of four rhombuses and the obtuse angles equal 180 less theacute angles. The characteristics of a scaffold may also be described byits surface area per volume. For a 1.0 mm×1.0 mm×1.0 mm solid cube, itssurface area is 6.0 square mm. When a 1.0 cubic mm structure iscomprised of a lattice structure rather than a 100 percent volumetricdensity material, the surface area per volume can increasesignificantly. In low volumetric density scaffolds, the surface area pervolume increases as the volumetric density increases. In someembodiments, a scaffold with a volumetric density of 30.1 percent wouldhave a surface area of 27.4 square mm per cubic mm. In some embodiments,if the volumetric density was decreased to 27.0 percent, the latticewould have a surface area of 26.0 square mm per cubic mm and if thevolumetric density were decreased to 24.0 percent, the lattice wouldhave a surface area of 24.6 square mm per cubic mm.

The MRDD and RDDR structures disclosed herein also have the advantage ofan especially high modulus of elasticity for a given volumetric density.When used as a lattice or scaffold, an implant with an adequate modulusof elasticity and a low volumetric density can be achieved. A lowvolumetric density increases the volume of the implant available forbone ingrowth.

In Table 1, below, are a number of example lattice configurations ofvarious lattice design elastic moduli. An approximate actual elasticmodulus was given for each example, representing a calculated elasticmodulus for that lattice after going through the manufacturing process.The lattice structures and implants disclosed herein can be designed toa design elastic modulus in some embodiments and to an approximateactual elastic modulus in other embodiments. One advantage of thepresently disclosed lattice structures is that the approximate actualelastic modulus is much closer to the design elastic modulus than hasbeen previously achieved. During testing, one embodiment of a latticewas designed for a 4.0 GPa design elastic modulus. Under testing, thelattice had an actual elastic modulus of 3.1 GPa, achieving an actualelastic modulus within 77 percent of the design elastic modulus.

For each lattice design elastic modulus, a volumetric density, ratio ofdesign elastic modulus to volumetric density, surface area in mm², ratioof surface area to volumetric density and ratio of surface area tolattice design elastic modulus is given.

TABLE 1 Table of example lattice structures based on lattice designelastic modulus in GPa Ratio of Surface Lattice Design Approx. ActualVolumetric Ratio of Design Surface Ratio of Surface Area to LatticeElastic Modulus Elastic Modulus Density Elastic Modulus to Area Area toVolumetric Design Elastic (GPa) (GPa) (percent) Volumetric Density (mm²)Density Modulus 0.3 0.233 18.5 1.6 22.5 121.5 74.9 3 2.33 29.9 10.0 27.592.2 9.2 4 3.10 33.4 12.0 28.8 86.4 7.2 5 3.88 36.4 13.8 29.9 82.2 6.0 64.65 38.8 15.5 30.7 79.1 5.1 7 5.43 40.8 17.2 31.3 76.9 4.5 8 6.20 42.119.0 31.8 75.4 4.0 9 6.98 43.2 20.8 32.1 74.3 4.0

In some of the embodiments disclosed herein, the required strutthickness can be calculated from the desired modulus of elasticity.Using the following equation, the strut thickness required to achieve aparticular elastic modulus can be calculated for some MRDD and RDDRstructures:Strut Thickness=(−0.0035*(E{circumflex over ( )}2))+(0.0696*E)+0.4603

In the above equation, “E” is the modulus of elasticity. The modulus ofelasticity can be selected to determine the required strut thicknessrequired to achieve that value or it can be calculated using apreselected strut thickness. The strut thickness is expressed in mm andrepresents the diameter of the strut. The strut thickness may becalculated using a preselected modulus of elasticity or selected todetermine the modulus of elasticity for a preselected strut thickness.

In some embodiments, the unit cell can be elongated in one or moredirections to provide a lattice with anisotropic properties. When a unitcell is elongated, it generally reduces the elastic modulus in adirection normal to the direction of the elongation. The elastic modulusin the direction of the elongation is increased. It is desirable toelongate cells in the direction normal to the direction of new bonegrowth contained within the interconnections, openings and central voids(if any). By elongating the cells in a direction normal to the desireddirection of reduced elastic modulus, the shear strength in thedirection of the elongation may be increased, providing a desirable setof qualities when designing a structural scaffold. Covarying the overallstiffness of the scaffold may augment or diminish this effect, allowingvariation in one or more directions.

In some embodiments, the sub-unit cells may be designing by controllingthe height of the node relative to the height of the volume that definesthe sub-unit cell. Controlling the height of the node can impact thefinal characteristics and appearance of the lattice structure. Ingeneral, increasing the height of the node increases the strutthickness, increases the volumetric density, increases the strength andincreases the elastic modulus of the resulting lattice. When increasingthe height of the node, the width of the node can be held constant insome embodiments or varied in other embodiments.

In some embodiments, the sub-unit cells may be designing by controllingthe volume of the node relative to the volume that defines the sub-unitcell. Controlling the volume of the node can impact the finalcharacteristics and appearance of the lattice structure. In general,increasing the volume of the node increases the strut thickness,increases the volumetric density, increases the strength and increasesthe elastic modulus of the resulting lattice. When increasing the volumeof the node, the width or height of the node could be held constant insome embodiments.

In Table 2, below, are a number of example lattice configurations ofvarious lattice design elastic moduli. An approximate actual elasticmodulus was given for each example, representing a calculated elasticmodulus for that lattice after going through the manufacturing process.The lattice structures and implants disclosed herein can be designed toa design elastic modulus in some embodiments and to an approximateactual elastic modulus in some embodiments. For each lattice designelastic modulus, a lattice approximate elastic modulus, a node height, avolumetric density, a node volume, a ratio of node height to volumetricdensity, a ratio of node height to lattice design elastic modulus and aratio of volumetric density to node volume is given.

TABLE 2 Table of example lattice structures based on lattice designelastic modulus in GPa Lattice Design Lattice Approx. Node VolumetricNode Ratio of Ratio of Node Height Ratio of Vol. Elastic Modulus ActualElastic Modulus Height Density Volume Node Height to Lattice DesignDensity to (GPa) (GPa) (mm) (percent) (mm3) to Vol. Density ElasticModulus Node Volume 0.30 0.23 0.481 18.5 0.0185 2.60 1.60 9.98 3.00 2.330.638 29.9 0.0432 2.14 0.21 6.91 4.00 3.10 0.683 33.4 0.0530 2.05 0.176.29 5.00 3.88 0.721 36.4 0.0624 1.98 0.14 5.82 6.00 4.65 0.752 38.80.0709 1.94 0.13 5.48 7.00 5.43 0.776 40.8 0.0779 1.90 0.11 5.23 8.006.20 0.793 42.1 0.0831 1.88 0.10 5.07 9.00 6.98 0.807 43.2 0.0877 1.870.09 4.93

Some embodiments of the disclosed lattice structures are particularlyuseful when provided within an elastic modulus range between anincluding 0.375 GPa to 4 GPa. Some embodiments, more preferably, includea lattice structure with an elastic modulus between and including 2.5GPa to 4 GPa. Some embodiments include a lattice structure with avolumetric density between and including five percent to 40 percent.Some embodiments, more preferably, include a lattice structure with avolumetric density between and including 30 percent to 38 percent.

The lattice structures disclosed herein have particularly robust loadingand fatigue characteristics for low volumetric density ranges and lowelastic moduli ranges. Some embodiments of the lattice structures have ashear yield load and a compressive yield load between and including 300to 15000N in static and dynamic loading up to 5,000,000 cycles at 5 Hz.Some embodiments have a compressive shear strength and an axial loadbetween and including 300 to 15000N in static and dynamic loading up to5,000,000 cycles at 5 Hz. Some embodiments have a shear strength and anaxial load between and including 300 to 15000N in static and dynamicloading up to 5,000,000 cycles at 5 Hz. Some embodiments have atorsional yield load up to 15 Nm.

In one example, the inventive lattice structure has a volumetric densityof between and including 32 percent to 38 percent, an elastic modulusbetween and including 2.5 GPa to 4 GPa and a shear strength and an axialload between and including 300 to 15000N in static and dynamic loadingup to 5,000,000 cycles at 5 Hz. Some examples include a first set ofsubstantially homogeneous openings with a width of about 200 μm to 900μm and a second set of substantially homogenous openings with a width ofabout 1 to 15 times the width of the first set of openings, where thenumber of openings in the second set are provided at a ratio of about1:8 to 1:12 relative to the number of openings in the first set.

The disclosed structures can also have benefits when used inapplications where osteointegration is not sought or undesirable. Byincluding a growth inhibiting coating or skin on a structure, thelattice disclosed herein can be used to provide structural supportwithout providing a scaffold for bone growth. This may be desirable whenused in temporary implants or medical devices that are intended to beremoved after a period of time.

Disclosed herein is a first exemplary embodiment of a fixation plate 10configured for use with an exemplary implant 20. The fixation plate canbe configured to work with multiple types of implants, including but notlimited to, bone fusion implants and interbody fusion implants. In someembodiments, the implant 20 is a cervical stand-alone (hereinafter“CSA”) implant. In some embodiments, the implant 20 is an AnteriorLumbar Interbody Fusion Stand-Alone (hereinafter “ALIF-SA”) implant. Insome embodiments, the implant 20 is a Posterior Lumbar Interbody Fusion(hereinafter “PLIF”) implant. In some embodiments, the implant 20 is aTransforaminal Lumbar Interbody Fusion (hereinafter “TLIF”) implant. Insome embodiments, the implant 20 is a PLIF or TLIF implant. In someembodiments, the implant 20 is an Anterior Lumbar Interbody Fusion(hereinafter “ALIF”) implant. In some embodiments, the implant 20 is avertebral body replacement (hereinafter “VBR”) implant. In someembodiments, the implant 20 is an osteotomy wedge. In some embodiments,the implant 20 is an ankle fusion spacer implant. In some embodiments,the implant 20 is configured for tissue attachment, tissue including butnot limited to bony structures and connective tissue. In someembodiments, the implant 20 is configured to allow tissue in-growth,tissue including but not limited to bony structures and connectivetissue.

The fixation plate 10 can be configured to allow motion relative to animplant after implantation and/or relative to a patient's tissue afterimplantation. In some embodiments, the fixation plate can allow axialcompression relative to an implant after implantation. In the embodimentof the fixation plate presented, the fixation plate can be attached tothe implant so that the fixation plate has at least one degree offreedom relative to the implant. The fixation plate can also be attachedto a first bone and/or a second bone, each attachment with at least onedegree of freedom. In some embodiments, the fixation plate can beattached to an implant and/or tissue so that the fixation plate has morethan one degree of freedom relative to its respective attachment point.In some embodiments, the fixation plate can be attached to a first boneand/or a second bone with a conical degree of freedom.

Some embodiments of the fixation plate have screw holes with a concaveprofile and are attached to a patient's bone using a bone screw with ascrew head having a convex profile, corresponding to the concave profileof the screw holes, when viewed from the side on the end of the screwhead oriented towards the threaded portion. The use of a screw head witha convex profile and a screw hole with a concave profile can provide afixation with at least a conical degree of freedom. The bone screw headcan also be fixed relative to the fixation plate screw holes with aclearance fit of greater than zero that can provide, in some respects,an amount of translational motion and prevent binding between the bonescrew head and fixation plate screw holes. A clearance fit, as usedherein, refers to a condition where there is a positive differencebetween the dimensions of assembled components. For example, a clearancefit would be present when the diameter of a screw head is less than itscorresponding screw hole.

The fixation plate can be attached to an implant using a fastening meanswith at least one degree of freedom. Some embodiments of the fixationplate use a fastening means with a clearance fit of greater than zerobetween the fixation plate and an implant. The use of a fastening meanswith a clearance fit can provide, in some respects, an amount oftranslational motion and prevent binding between the fixation plate, theimplant and/or the fastening means. Some fastening means that could beused include, but are not limited to, quarter turn fasteners, screws,etc. A clearance fit with respect to a quarter turn fastener can be inan axial and/or radial direction, providing multiple directions fortranslational motion.

The number of degrees of freedom provided between two given componentscan be the result of multiple factors, including but not limited to, adesigned degree of freedom, a manufacturing tolerance degree of freedomor a clearance fit degree of freedom. The disclosure focuses on adesigned degree of freedom and, in some embodiments, an intendedclearance fit degree of freedom. However, it is appreciated thatmanufacturing tolerances can be measured and/or measured and usedsimilarly to create a device with the necessary degree(s) of freedom.

In FIG. 1R is a side view of the fixation plate 10 rotatably attached toan implant 20. One bone screw 30 is pictured, however the fixation plate10 is configured for two bone screws to be used. In FIG. 1R, thefixation plate 10 is in a locked position relative to the implant 20. Alocked position, as used herein, refers to one element being fixed toanother element in at least one plane, but with freedom to move in atleast one plane. In FIG. 1R, the fixation plate 10 is fixed in theforward to rear direction relative to the implant 20 but is free torotation about an axis in the forward to rear direction. Forward andrear, are exemplary directions used to describe the drawings and are notintended to create any limitations as to use or configuration. In thedrawings used herein, the rear of the implant 20 refers to the end ofthe implant 20 configured to accept the fixation plate 10. The front ofthe implant 20 refers to the end opposite the rear. Portions of theimplant between the front and rear of the implant 20 can be described aslateral. The top to bottom direction of the implant 20 is described asthe axial direction or the direction of compression. While the exemplaryfixation plate 10 and implant 20 are configured for a situation wherethe axial direction and direction of compression are about the same,they do not need to be the same or similar.

In FIG. 2 is an isometric view of the fixation plate 10, implant 20 andbone screw 30 in a locked position. The fixation plate 10 can beconfigured to rotate relative to the implant 20 about an axis located inthe forward to rear direction. The angle of permitted rotation betweenthe fixation plate 10 and the implant 20 can be limited by theinterference between the implant 20 and a bone screw 30. The amount ofaxial compression permitted by the fixation plate 10 can be adjustedbased on the placement of the bone screws 30 relative to the implant 20.As the bone screws 30 are spaced away from the implant 20 axially, theamount of axial compression permitted increases to a certain point. Theamount of axial compression allowed can be approximated by the angle ofthe fixation plate 10 relative to the implant 20 after implantation fora fixation plate 10 of a particular length between screw holes 11. Forexample, a fixation plate 10 with 10 mm spacing between the screw holecenters 11 would allow more axial compression if implanted at an angleof 50 degrees relative to the implant 20 than if implanted at an angleof 45 degrees relative to the implant 20.

In some embodiments, the fixation plate 10 is oriented relative to theimplant 20 based on a line drawn between the centers of the screw holes11 relative to a plane passing through the axial center of the implant20. In some embodiments, the fixation plate 10 is oriented between andincluding −45 degrees and 45 degrees relative to the implant 20 in anunlocked position. In some embodiments, the fixation plate 10 isoriented between and including 10 degrees and 90 degrees relative to theimplant 20 in a locked position. In some embodiments, the fixation plateis oriented between and including −10 degrees and −90 degrees relativeto the implant 20 in a locked position.

In FIGS. 3 and 4 are additional views showing the relationship betweenthe fixation plate 10 and implant 20 in a locked position. While onlyone locked position is shown in the figures, it is appreciated that thefixation plate 10 could be rotated more or less relative to the implant20 in this and other embodiments.

In FIG. 4A is a side view of the fixation plate 10 and bone screws 30where hidden features are shown in broken lines. In some embodiments,the bone screws 30 can have a screw head 31 with a varying diameter thatcorresponds to a varying diameter of the screw holes 11. In someembodiments, the screw head 31 can have a convex profile when viewedfrom the side on the end of the screw head oriented towards the threadedportion 32. In some embodiments, the screw holes 11 can have a concaveprofile that corresponds to the convex profile of the screw head 31.

The use of a screw head 31 with a convex profile and a screw hole 11with a concave profile can provide a fixation with at least a conicaldegree of freedom 40. While the use of a screw head 31 with a convexprofile and a screw hole 11 with a concave profile is disclosed hereinto provide a fixation with a conical degree of freedom, it isappreciated that other methods exist in the art to achieve a fixationwith similar properties. In some embodiments, the conical degree offreedom is between zero degrees and 90 degrees. In some embodiments, theconical degree of freedom is between and including 10 degrees and 70degrees. In some embodiments, the conical degree of freedom is betweenand including 20 and 40 degrees. In some embodiments, the conical degreeof freedom is between and including 25 and 35 degrees. In someembodiments, the conical degree of freedom is between and including 28degrees and 32 degrees. In some embodiments, the conical degree offreedom is about 30 degrees.

The use of a screw head 31 with a convex profile and a screw hole 11with a concave profile can also provide a fixation with an infinitenumber of degrees of freedom. In some embodiments, the bone screw 30 isfixed to a segment of tissue so that there is a clearance fit 50 betweenthe screw head 31 and the screw hole 11. The clearance fit 50 allows thefixation plate 10 to rotate relative to the screw head 31 along anydesigned degree of freedom and an amount in the direction of theclearance fit 50. In some embodiments, it is desirable to use aclearance fit 50 of greater than zero between the screw head 31 and thescrew hole 11 to prevent binding.

In some embodiments, the screw holes 11 are circular and smoothinternally to allow the fixation plate 10 to rotate relative to the bonescrews 30. The screw holes 11 can have a single diameter or a diametergradient to accept specifically shaped bone screws 30. The screw holes11 and bone screws 30 can optionally be configured to include rotationalstops to constrain the rotation of the fixation plate 10 relative to abone screw 30.

In FIG. 5 is a side sectioned view of the fixation plate 10 and implant20 in an unlocked position. The fixation plate 10 further comprises acylindrical member 12 configured to fit within an attachment port 22 inthe implant 20. In some embodiments, the cylindrical member 12 andattachment port 22 further comprise a quarter locking mechanism usingthe partial rotation of the cylindrical member 12 or attachment port 22relative to one another to engage a pin, wedge or tip on either with asurface configured to receive a pin, wedge or tip.

In the exemplary embodiment, the attachment port 22 further comprises anouter portion 23 and an inner portion 24. In some embodiments, the outerportion 23 is cylindrical, having a smaller diameter than the innerportion 24, also being cylindrical. The outer portion 24 can have one ormore circular sectors where material has been removed in a radialdirection that corresponds to areas on the cylindrical member 12 wherematerial has been added in a radial direction. Material being added orremoved can refer to the design process of a device or a process duringmanufacturing so that a device with material added can refer to a singlecontinuous material and a device with material removed can refer to adevice as manufactured.

In FIG. 6 is a rear view of the fixation plate 10 and implant 20 in anunlocked position. In some embodiments, tool engagement areas 13 can beincluded on the fixation plate 10 to apply a torque to the fixationplate 10 during implantation. A tool with extensions corresponding tothe tool engagement areas 13 could be used to rotate the fixation plate10.

In FIG. 7 is a rear view of the implant 20 configured to receive thefixation plate 10. In the exemplary embodiment, the cylindrical member12 further comprises two pins 14 extending radially in oppositedirections. The implant 20, in this embodiment, is configured to acceptthe two pins 14 through the inclusion of cutouts 25 extending radiallyin opposite directions in the outer portion 23 of the attachment port22. It is appreciated that the disclosed configuration of pins andcutouts is merely one way to attach a fixation plate 10 to an implant 20in a way to allow an unlocked and a locked position. For example, feweror greater than two pins 14 could be used, fewer or greater than twocutouts 25 could be used, the pins 14 could be spaced apart on thecylindrical member 12 at an interval other than about 180 degrees andthe cutouts 25 could be spaced apart on the outer portion of theattachment port 22 at an interval other than about 180 degrees.

In FIG. 8 is a side sectioned view of the fixation plate 10 and implant20 in a locked position. In the locked position, the pins 24 extendingradially from the cylindrical member 12 provide a surface that is inexcess of the diameter of the outer portion 23 of the attachment port22. The pins 24 provide a surface that can be less than the diameter ofthe inner portion 24 of the attachment port 22 to allow the fixationplate 10 to rotate relative to the implant 20 without encumbrance. Whilethe inner portion 24 is shown as being cylindrical with a substantiallyequal diameter throughout, in some embodiments the inner portion 24 canbe non-cylindrical or have a varying diameter. In some embodiments, theinner portion 24 further comprises a varying diameter with at least onearea with a diameter smaller than the distance between the distal endsof the pins 24. In some embodiments, the inner portion 24 furthercomprises at least one area where material has been added to create alocalized area with a diameter smaller than the distance between thedistal ends of the pins 24. The use of areas with a diameter smallerthan the distance between the distal ends of the pins 24 can be used toprovide rotational stops for the fixation plate 10 relative to theimplant 20.

In FIG. 9 is an isometric sectioned view of the implant 20 configured toaccept the fixation plate 10. In FIG. 10 is a top sectioned view of theimplant 20 configured to accept the fixation plate 10. These figuresprovide additional views of the attachment port 22 and the exemplaryconfiguration using an outer portion 23, an inner portion 24 and cutouts25.

What has been described is a fixation plate and an implant configured toaccept the disclosed fixation plate. In this disclosure, there is shownand described only an exemplary embodiment of the invention, but, asaforementioned, it is to be understood that the invention is capable ofuse in various other combinations and environments and is capable ofchanges or modifications within the scope of the inventive concept asexpressed herein.

The invention claimed is:
 1. A medical implant system, comprising: abone fusion implant configured for implantation into a body, wherein thebone fusion implant comprises at least one side; one or more fastenersconfigured to fix the bone fusion implant to one or more bony structuresin the body; and an elongate plate comprising a plurality of openingsconfigured to allow passage of the one or more fasteners through theelongate plate, the elongate plate being rotationally fixed to a side ofthe bone fusion implant and configured to rotate relative to the bonefusion implant and allow axial compression relative to the bone fusionimplant after implantation into the body, wherein an amount of the axialcompression is adjustable based on placement of the one or morefasteners relative to the elongate plate and an angle of the elongateplate relative to the bone fusion implant.
 2. The medical implant systemof claim 1, wherein the plurality of openings are further configured torotate about the one or more fasteners.
 3. The medical implant system ofclaim 1, wherein the plurality of openings further comprise a smoothannular shape with a first diameter and each of the one or morefasteners further comprises a head with a smooth annular shape with asecond diameter; wherein the second diameter is less than the firstdiameter.
 4. The medical implant system of claim 1, wherein the bonefusion implant further comprises a forward and rear direction, a lateraldirection and an axial direction.
 5. The medical implant system of claim4, wherein the elongate plate further comprises a fixed position in aforward to rear direction relative to the bone fusion implant and isconfigured to rotate about an axis in the forward to rear direction ofthe bone fusion implant.
 6. The medical implant system of claim 1,wherein the elongate plate is configured to allow at least one degree offreedom relative to the bone fusion implant and the degree of freedomrelative to the bone fusion implant further comprises the axialdirection.
 7. The medical implant system of claim 1, wherein theelongate plate further comprises a quarter turn fastener extendingtowards the side of the bone fusion implant; and wherein the bone fusionimplant further comprises an opening corresponding to the quarter turnfastener located on the elongate plate.
 8. The medical implant system ofclaim 1, wherein the elongate plate is further translationally fixedrelative to the bone fusion implant in all directions and rotationallyfree in at least one direction relative to the bone fusion implant. 9.The medical implant system of claim 1, wherein the plurality of openingscomprise equidistantly distributed openings.
 10. The medical implantsystem of claim 9, wherein the amount of axial compression is a functionof an angle of the elongate plate relative to the bone fusion implantand a distance between at least two adjacent openings in the pluralityof openings.
 11. The medical implant system of claim 10, wherein theamount of axial compression is correlated with the angle of the elongateplate for the distance between the at least two adjacent openings in theplurality of openings.
 12. The medical implant system of claim 1,wherein an angle of rotation of the elongate plate relative to the bonefusion implant is a function of an interference between the bone fusionimplant and the one or more fasteners through the elongate plate. 13.The medical implant of claim 1, wherein the elongate plate is configuredto allow at least one degree of freedom relative to the bone fusionimplant.